1. Field of the Invention
The present invention relates to an anisotropic nanophase composite material consisting of particulates of dimensions on the order of nanometers and showing several anisotropic physical properties such as an anisotropic nonlinear optical effect, birefringence, polarization, or a photovoltaic effect. The invention also relates to a method of producing such a composite material.
2. Description of the Related Art
Utilization of a nonlinear optical effect or polarization of composite materials in which structural units of dimensions on the order of nanometers such as metal particles or semiconductor crystallites are dispersed has been discussed.
We now describe nonlinear optical effects. When light of electric field E and oscillation frequency .omega. is incident on a substance, a wave of polarization of the frequency .omega. is induced in proportion to the electric field E in the substance. Then, light of the oscillation frequency .omega. originates from the wave of polarization. This is normal interaction of light with a substance, and the incident light is identical in oscillation frequency with the outgoing light. In some particular substances, however, light of electric field E and oscillation frequency .omega. induces considerably intense waves of polarization proportional to E.sup.n. Substances of this nature are called nonlinear optical media. These substances show the following peculiar phenomena. They produce light having an oscillation frequency n times as high as the oscillation frequency of the incident light, i.e., the outgoing light shows a color different from that of the incident light. The refractive index of such a nonlinear optical medium may change as a function of the intensity of the light, or the square of the electric field. These are collectively known as nonlinear optical effects. Application of nonlinear optical effects to wavelength conversion of laser radiation and to optical logic devices has been discussed. Such a nonlinear optical effect is closely related to the quantum confinement effect described below.
Where the dimensions of metal or semiconductor particulates are of the order of nanometers, quantum particles which are involved in the interaction of light with a substance, such as electrons, holes and excitons, are hindered from moving freely. As a result, they produce peculiar phenomena not encountered in bulk state. This is called a quantum confinement effect. It is known that when this effect is produced, a strong nonlinear optical effect is developed. For this reason, the media in which the above-described particulates are dispersed and substances having structural features of dimensions on the order of nanometers are regarded as promising nonlinear optical materials and have been continuous subjects of investigation.
A method of producing a composite material in which particulates having dimensions of the order of nanometers and exhibiting a nonlinear optical effect are dispersed is described in New Glass, Vol. 3, No. 4, 41 (1989). In this method, glass and the material made up of particulates of dimensions on the order of nanometers are mixed up and melted. Then, the molten mixture is annealed again at an appropriate temperature so that the microscopic particulates may precipitate in the glass. Another method of producing a composite material in which particulates of dimensions on the order of nanometers are dispersed is described in Optical and Electro-Optical Engineering Contact (in Japanese), Vol. 27, No. 7, 389 (1989). In particular, glass and a material to be involved in glass matrix as particulates having dimensions of the order of nanometers are simultaneously evaporated onto a substrate, to form thin glass films with the aforementioned microscopic particulates dispersed therein. In this way, the composite material is produced with or without subsequent annealing.
Even in a medium in which structural units of dimensions on the order of nanometers such as crystallites are dispersed, a strong nonlinear optical effect is not effectively obtained from the whole medium unless the nonlinear optical effects produced by the individual particulates add together. In the composite materials produced by the above-described methods, the particulates of dimensions on the order of nanometers vary greatly in size. Also, their crystallographic axes are not aligned. Therefore, the latent potentials of nonlinear optical effect have not been fully realized yet, as reported by Survey of the Technologies on Measurement, Evaluation, and Control of Elementary Functions in Microscopic Regions of Materials (in Japanese), a report on research and investigation committed by the Japanese Science and Technology Agency in 1988, supervised by the General Research Department of the Research and Development Bureau of the Japanese Science and Technology Agency.